SYNTHESIS AND CHARACTERIZATIONS OF
YBa
2Cu
3O
7-δSUPERCONDUCTOR WITH ADDED
Al
2O
3NANOPARTICLES VIA
CITRATE-NITRATE AUTO-COMBUSTION REACTION
MOHD SHAHADAN BIN MOHD SUAN
THESIS SUBMITTED IN FULFILMENT
OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
FACULTY OF ENGINEERING
UNIVERSITY OF MALAYA
KUALA LUMPUR
ii
UNIVERSITI OF MALAYA
ORIGINAL LITERARY WORK DECLARATION
Name of Candidate: Mohd Shahadan Bin Mohd Suan (IC No.: 850918-06-5483)
Registration/ Matrix No.: KHA 100026
Name of Degree: The Degree of Doctor of Philosophy
Title of υroject υaper/ Research Report/ Dissertation/ Thesis (“this Work”): Synthesis and characterizations of YBa2Cu3O7-δ superconductor with added Al2O3 nanoparticles via citrate-nitrate auto-combustion reaction.
Field of Study: Superconductor Material
I do solemnly and sincerely declare that:
(1) I am the sole author/ writer of this Work;
(2) This work is original;
(3) Any use of any work in which copyright exists was done by way of fair dealing and for permitted purposes and any excerpt or extract from, or reference to or reproduction of any copyright work has been disclosed expressly and sufficiently and the title of the work and its authorship have been acknowledged in this Work;
(4) I do not have any actual knowledge nor do I ought reasonably to know that the making of this work constitutes an infringement of any copyright work;
(5) I hereby assign all and every rights in the copyright to this Work to the University of Malaya (“UM”), who henceforth shall be owner of the copyright in this Work and any reproduction or use in any form or by any means whatsoever is prohibited without the written consent of UM having been first had and obtained;
(6) I am fully aware that if the course of making this Work I have infringed any copyright whether intentionally or otherwise, I may be subject to legal action or any other action as may be determined by UM.
Candidate‟s Signature Date
Subscribed and solemnly declared before,
Witness‟s Signature Date
Name:
iii
ABSTRACT
Superconductor materials are renowned to conduct electricity at zero resistance and
capable to expel magnetic flux. It can be used in developing efficient wire cables,
magnetic energy storage and levitation technologies. Thus, the high temperature
superconductor YBa2Cu3O7-δ with added Al2O3 nanoparticles was synthesized via
citrate-nitrate auto-combustion reaction process. The novelty of this research work is the
citrate-nitrate auto-combustion reaction method consumed less energy and time
compared with other conventional synthesis methods for processing of composite
superconductor oxides and produced well distribution of Al2O3 nanoparticles in YBa2Cu3O7-δ superconductor. The auto-combustion reaction transformed the formulated precursor citrate-nitrate gel into very fine ashes. It yielded Al2O3 and YBa2Cu3O7-δ phases after calcination process which was further heat treated to achieve
superconductivity. The reactions during synthesis processes were investigated through
the thermal evaluations. The effects of different concentration of Al2O3 nanoparticles on the structure, superconducting, magnetic and mechanical properties of YBa2Cu3O7-δ
were investigated and appraised. The sustained orthorhombic structure in each sample
contributed to consistency in superconducting transition temperature while the flux
pinning forces provided by the non-superconducting nanoparticles improved the critical
current density. Furthermore, the mechanical hardness of the samples was also
influenced by the addition of nanoparticles. This work shows that the citrate-nitrate
iv
SINTESIS DAN PENCIRIAN SUPERKONDUKTOR YBa2Cu3O7-δ DITAMBAH
ZARAH NANO Al2O3 MELALUI TINDAK BALAS PEMBAKARAN
-AUTOMATIK SITRAT-NITRAT.
ABSTRAK
Bahan-bahan superkonduktor telah diketahui dapat mengalirkan arus elektrik pada
rintangan sifar dan menyingkir fluks magnet. Ia boleh digunakan dalam membangunkan
teknologi wayar kabel efisien, penyimpanan tenaga dan pengapungan magnet. Oleh itu,
superkonduktor suhu tinggi YBa2Cu3O7-δ terkandung zarah nano Al2O3 telah disintesis melalui tindak balas pembakaran-automatik sitrat-nitrat. Keaslian kerja penyelidikan ini
ialah kaedah sintesis ini lebih menjimatkan tenaga dan masa berbanding kaedah lama
dalam penghasilan komposit superkonduktor oksida dan dapat menghasilkan serakan
seragam zarah nano Al2O3 dalam superkonduktor YBa2Cu3O7-δ. Pembakaran-automatik telah menukarkan gel sitrat-nitrat yang telah diformulasi kepada abu-abu yang sangat
halus. Ianya menjadi fasa-fasa Al2O3 dan YBa2Cu3O7-δ setelah dikalsin sebelum
dirawathaba bagi mencapai kesuperkonduksian. Setiap tindak balas yang berlaku
semasa proses sintesis ini diperincikan melalui kaedah penilaian terma. Segala kesan
akibat penggunaan kepekatan berbeza zarah nano Al2O3 terhadap struktur, sifat kesuperkonduksian, kemagnetan dan sifat mekanikal YBa2Cu3O7-δ dikaji dan
ditaksirkan. Struktur ortorombik setiap sampel menyumbang kepada suhu peralihan
kesuperkonduksian yang konsisten manakala daya pengepin yang diperolehi daripada
zarah nano bukan superkonduktor telah menambahbaik ketumpatan arus genting. Selain
itu, kekerasan mekanikal sampel-sampel juga telah terpengaruh dengan penambahan
zarah nano ini. Kajian ini menunjukkan bahawa kaedah pembakaran-automatik
v
ACKNOWLEDGMENT
Foremost I wish to express my sincere appreciation to my supervisor, Dr. Mohd Rafie
Johan for his consistent guidance, teaching and supervision during the process of
working this research. His advice and comments have helped me significantly in
moving forward and completing this thesis report on time. I could not have imagined
having better supervisor and mentor during my PhD study.
I would also thank Dr. Yoichi Kamihara from Keio University, Japan for
offering me an internship opportunity to work in his research group in Hiyoshi, Japan.
This internship program has enlighten me and allowed me to work on diverse exciting
project. To my friends in Keio University, you have made my stay in Japan a
memorable one.
Besides, I would like to thank my friends in Nanomaterials Group of Advanced
Materials lab, Mechanical Engineering of University of Malaya. I thank them for their
continuous support and assistance provided whenever I needed a helping hand. A
special thanks to Mr. Nazarul Zaman, Mr. Said Sakat and Mrs. Norzirah, a big
contribution and assistances from them are very great indeed.
Last but not least, my deepest gratitude goes to my beloved parents, Mohd Suan
Tulis and Shariah Dahol and all my siblings, for their endless love and encouragement. I
will not be who I am today without their encouragement. Not to forget endless support
and understanding from my wife, Vizy Nazira Riazuddin and my little prince,
Muhammad Eusoff Muzaffar. To those who indirectly contributed in this research, your
vi
TABLE OF CONTENTS
ORIGINAL LITERARY WORK DECLARATION ii
ABSTRACT iii
ABSTRAK iv
ACKNOWLEDGEMENTS v
TABLE OF CONTENTS vi
LIST OF FIGURES xi
LIST OF TABLES xvii
LIST OF SYMBOLS AND ABBREVIATIONS xviii
CHAPTER 1: INTRODUCTION 1
1.1 Research background 1 1.2 Problems statement 2
1.3 Research objectives 5
1.4 Scope of the works 6
1.5 Significant of research 7
CHAPTER 2: LITERATURE REVIEW 8
2.0 Superconductivity 8
2.1 Zero resistivity of superconductor 9
2.2 Perfect diamagnetism 11
vii
2.3.1 London penetration depth 13
2.3.2 υippard‟s non-local theory 17
2.3.3 Ginzburg-Landau theory 18
2.4 Type II superconductor 21
2.4.1 Critical current density 21
2.4.2 Flux pinning 22
2.4.3 Bean model 24
2.4.4 Extended Bean model 27
2.5 YBa2Cu3O7-δ superconductor 29
2.5.1 Addition of nanoparticles in bulk YBa2Cu3O7-δ 32 2.5.2 Addition of Al2O3 nanoparticles into YBa2Cu3O7-δ 34
2.6 Synthesis of YBa2Cu3O7-δ powder 37
2.7 Synthesis of Al2O3 nanoparticles 38
2.8 Combustion synthesis 39
2.8.1 Citrate-nitrate auto-combustion reaction 44
CHAPTER 3: METHODOLOGY 49
3.1 Materials 49
3.2 Sample preparation 50
3.2.1 Citrate to nitrate ratio dependence mixture solution 50
3.2.2 Al2O3 added YBa2Cu3O7-δ mixture solution 51 3.2.3 Auto-combustion reaction of the gel 52
3.2.4 Calcination and sintering process 53
viii 3.3.1 Thermogravimetric analysis (TGA) and differential thermal
analysis (DTA) 55
3.2.2 X-ray diffraction (XRD) 55
3.2.3 Field emission scanning electron microscopy (FESEM) and
energy dispersive X-ray (EDX) 57
3.2.4 Resistivity measurement 58
3.2.5 Defining critical temperature (TC) 60
3.2.6 Magnetisation measurement 61
3.2.7 Magnetic critical current density (JC) 62
3.2.8 Hardness test 63
3.2.9 Summary 63
CHAPTER 4: EFFECTS OF CITRATE NITRATE RATIO 65
4.1 Decomposition characteristics 65
4.2 YBa2Cu3O7-δ structural properties 72
4.3 Microstructure and EDX of YBa2Cu3O7-δsamples 80
4.4 Critical temperature (TC) analysis 85
4.5 Discussions 87
CHAPTER 5: EFFECTS OF THE ADDITION OF Al2O3
NANOPARTICLES 89
5.1 Decomposition characteristics 89
ix
5.4 Microhardness of Al2O3 added YBa2Cu3O7-δ 118
5.5 Electrical resistivity and critical temperature (TC) analysis 120 5.6 Magnetic hysteresis and critical current density (JC) analysis 123
5.7 Discussions 130
CHAPTER 6: CONCLUSIONS 132
6.1 Effects of citrate-nitrate ratio 132
6.2 Effects of the addition Al2O3 nanoparticles 132
6.3 Future works 133
REFERENCES 135
LIST OF PUBLICATIONS AND PRESENTED PAPERS 145
Academic Journals 145
Conference Proceedings 146
Conference Presentations 146
APPENDIX A1 147
Refined XRD pattern (xmol = 0.00 and 0.02)
APPENDIX A2 148
x
APPENDIX A3 149
xi
LIST OF FIGURES
Figure 2.1 Progress of TC according to year discovered( Roslan, 2004). 9 Figure 2.2 Temperature dependence BC relation depicts boundary that
separate between superconducting and normal state. 11
Figure 2.3 Temperature dependence BC1 and BC2 of type II
superconductor. 12
Figure 2.4 Penetration of magnetic field into superconductor, B(x) as
determined from equation (2.16). The B (0) is the field on
the surface of superconductor. After the L of
superconductor, B no longer exists. 17
Figure 2.5 Internal profiles for the slab superconductor magnetized in a
parallel field to its surface of thickness D; (a) local fields and
(b) current distribution for fields 0, H*/2, H* and 2H*
(Bean, 1964). 24
Figure 2.6 Internal profiles of the slab superconductor after the
magnetic field (H0) is removed; (a) local fields, and (b) perpendicular to surface having of dimensions l x t (Gyorgy
et al., 1989). 27
xii Figure 2.10 Lattice parameters for YBa2Cu3O7-δ with different δ (Cava et
al., 1990). 31
Figure 2.11 Oxygen deficiencies, δ dependence TC for various
YBa2Cu3O7-δ samples. 31
Figure 2.12 Enthalpy-temperature plot for reactants and products in
combustion reaction system (Moore and Feng, 1995). 42
Figure 3.1 Physical appearance of samples; (a) as-prepared mixture
solution, (b) gel, (c) flammable combustion and (d) ashes
product. 52
Figure 3.2 Physical appearances of the resultant powders; (a) before
calcination, and (b) after calcination. 53
Figure 3.3 Pellet sample ready for characterizations after sintering
process. 53
Figure 3.4 Calcination profiles of the ashes product. 54
Figure 3.5 Sintering profiles of the pellet samples. 54
Figure 3.6 Rigaku RINT2500Ultra18 XRD machine. 56
Figure 3.7 Crystal structures are drawn using „VESTA 3 program for
three-dimensional visualisation of crystal, volumetric and
morphology data‟ (Momma and Izzumi, 2011). 57
Figure 3.8 Zeiss Auriga Ultra 40 XB FESEM machine. 58
Figure 3.9 Sample holder set up for resistivity measurement. 59
Figure 3.10 Closed cryogen chamber model SRDK-101D. 60
Figure 3.11 Determination of TC onset and TC zero from temperature
dependence resistivity curve. 61
Figure 3.12 Sample holder set up for field dependence magnetization
xiii Figure 3.13 SQUIDs (Quantum Design Co. LTD; MPMS-XL) for
magnetic properties measurement. 62
Figure 3.14 Flow chart for the preparation and characterization of Al2O3
nanoparticles added YBa2Cu3O7 samples. 64
Figure 4.15 EDX spectra of samples for different values of c/n; (a) 0.3,
xiv Figure 4.16: Temperature dependence resistivity of YBa2Cu3O7-δ samples
with different c/n values. 88
Figure 5.5 XRD pattern of YBa2Cu3O7-δ and Al2O3 nanoparticles added
YBa2Cu3O7-δ samples. Black and pink bars at bottom show
Bragg diffraction pattern for YBa2Cu3O7-δ and Al2O3
respectively. 97
Figure 5.6 Refined XRD pattern of sample without Al2O3 nanoparticles
(xmol = 0.00). 98
Figure 5.7 Intensity difference patterns for various compositions of
Al2O3 nanoparticles added YBa2Cu3O7-δ samples. 99
Figure 5.8 XRD pattern of Al2O3 ashes.
101
Figure 5.9 XRD pattern of crystalline Al2O3 after calcined at 900 °C for
1h. 101
Figure 5.10 The a and b lattice constants of the samples. Error bars show
standard deviation of lattice constant value. 104
Figure 5.11 Orthorhombicity of pure YBa2Cu3O7-δ and Al2O3 added YBa2Cu3O7-δ. Error bars show standard deviation of
xv Figure 5.12 The c lattice constants of the samples. Error bars show
standard deviation of c lattice constant. 105
Figure 5.13 Crystallite sizes of YBa2Cu3O7-δ and Al2O3 added
Figure 5.19 EDX spot analysis pointed on nanoparticles; (a) xmol = 0.02, (b) xmol = 0.04, (c) xmol = 0.06, (d) xmol = 0.08 and (e) xmol =
0.10. 114
Figure 5.20 Microstructure of the intersection of YBa2Cu3O7-δ for sample
with xmol = 0.06. 116
Figure 5.21 Vickers microhardness of YBa2Cu3O7-δ and Al2O3 added
YBa2Cu3O7-δ samples. 118
Figure 5.22 Temperature dependence resistivity of YBa2Cu3O7-δ and
Al2O3 added YBa2Cu3O7-δ samples. 120
Figure 5.23 Critical temperatures of YBa2Cu3O7-δ and Al2O3 added
YBa2Cu3O7-δ samples. 121
Figure 5.24 Field dependent magnetization, M-H hysteresis loop of
xvi Figure 5.25 Field dependent magnetization, M-H hysteresis loop of
YBa2Cu3O7-δ and Al2O3 added YBa2Cu3O7-δ samples at 77 K. 124 Figure 5.26 Magnetic JC of YBa2Cu3O7-δ and Al2O3 added YBa2Cu3O7-δ
samples at 5 K. 127
Figure 5.27 Magnetic JC of YBa2Cu3O7-δ and Al2O3 nanoparticles added
YBa2Cu3O7-δ samples at 77 K. 128
Figure 5.28 JC of YBa2Cu3O7-δ and Al2O3 added YBa2Cu3O7-δ samples at
xvii
LIST OF TABLES
Table 2.1 Critical parameters of YBa2Cu3O7-δ superconductor (Roslan,
2004). 32
Table 2.2 TC and JC of Al2O3 nanoparticles added YBa2Cu3O7-δ
obtained from various studies. 36
Table 2.3 Comparison of the properties of YBa2Cu3O7-δ produced
using various processing techniques (Pathack et al., 2004). 47
Table 3.1 Raw materials used to prepare stock solutions. 50
Table 3.2 Citrate-nitrate ratio (c/n) composition. 51
Table 3.3 Labels of as-prepared solution varied by Al(NO3)3
compositions. 51
Table 4.1 Temperature dependence decomposition behavior and
reaction of the gel samples during auto-combustion reaction. 68
Table 4.2 Atomic numbers and ratio of the elements obtained from
EDX analysis of the YBa2Cu3O7-δ for different c/n values. 85
Table 5.1 Reaction and weight loss of the Al(NO3)3 added gel samples
at varied steps. 96
Table 5.2 Elemental analysis of YBa2Cu3O7-δ structure and Al2O3
xviii
LIST OF SYMBOLS AND ABBREVIATIONS
Symbol Description
a lattice constant at x direction
A cross section of the sample
b lattice constant at y direction
Ba applied magnetic field
BC critical magnetic field
Bi interior magnetic field
Br remnant flux density
c lattice constant at z direction
c/n citrate to nitrate ratio
FESEM field emission scanning electron microscope
xix
Fn free energy at normal state
Fp pinning force
fp basic pinning force
Fs free energy at superconducting state
H (P) heat required by products
H (R) heat required by reactants
BC, HC critical magnetic field
BC2, HC2 upper critical applied magnetic field HV Vickers hardness
JC critical current density
Js density of superconducting current
kB Boltzmann‟s constant
ni stoichiometry ratio of reactants coefficient
nj stoichiometry ratio of products coefficient
xx
Vf volume fraction of pinning center
vs velocity of superconducting electron
xmol concentration of Al2O3 nanoparticles in the sample
XRD X-ray diffraction
YSZ yttrium stabilized zirconia
ΔE energy gap of Cooper pair fluid
ΔH heat needed for ignition
ΔM magnetization gap
ΔQ heat loss
λ penetration depth
xxi ξ superconductors coherence length
ξab coherence length parallel to a-b plane
ξc coherence length parallel to c plane
ξo intrinsic coherence length
ρ resistivity
conductivity
crystallite size
ψ superconducting order parameter
1
CHAPTER 1
INTRODUCTION
1.1 Research background
Superconductivity is a promising technology to prevent energy losses attributed
from electrical resistivity. This technology attracts much attention to the researches due
to two main reasons: the electricity can be conducted at zero resistivity and the magnetic
flux can be totally repelled out from the body of superconducting material. Since
discovered in 1911, superconductivity was only been found in elements and alloys
where the critical temperature (TC) of these materials are very low (Onnes, 1991). In 1986, the lanthanum cuprate was found to be the first compound material to exhibit
superconductivity (Muller and Bednorz, 1986). This breakthrough was followed by
discovery of yttrium barium copper oxide (YBa2Cu3O7-δ) superconducting compound in 1987 which brought a great excitement within the scientific community because this
material can conduct electricity without having resistivity at temperatures above 77 K.
This is the temperature at which nitrogen liquefies, thus YBa2Cu3O7-δ changed the
perspective of the applications of superconductivity and opened up the possibility for
numerous advancements of technologies (Wu et al., 1987).
Categorized as type II superconductor, YBa2Cu3O7-δ shows perfect diamagnetism at below lower critical fields (HC1), allows penetration of quantized magnetic flux (vortex) at higher fields, and loss superconductivity at above higher
2 practical to be used in stronger magnetic fields compared with conventional
superconductors.
1.2 Problems statement
Theoretically, YBa2Cu3O7-δ has excellent ability to carry higher critical current
density (JC) due to having very high HC2 compared with HC1. However, when electrical current is flowed in applied magnetic field of HC1 < H < HC2, the interaction between vortex and current flow results in the motion of vortex due to Lorentz force which can
cause energy loss. At this point, only a small density of current limits by JC is permitted to flow through this superconductor before losing energy. Generally the JC can be increased if the vortex is prevented from moving. This can be achieved by pinning them
with suitable non-superconducting point as known as pinning centre materials. Pinning
centre materials in YBa2Cu3O7-δ can be created either by inducing defects through irradiation techniques and chemical doping or by introducing second phase particles
having nanometer size. In chemical doping, elements such as calcium (Ca), potassium
(K), silver (Ag) and aluminium (Al) are diffused into YBa2Cu3O7-δ structure (Giri et al., 2005, Celebi et al., 2000, Sen et al., 1990 and Zhang et al., 1995). These elements
locally modify the crystallinity of the structure and generate defects such as twins,
tweed, and inhomogeneous micro-defects to pin the vortices. The JC can be improved by chemical doping but in return this method may reduce the TC, since the orthorhombicity of YBa2Cu3O7-δ is being altered; hence, decreased.
Thus for some reasons, introduction of nanoparticles in YBa2Cu3O7-δ has generated a great interest among researchers. This method represents an easy controlled,
3 superconducting properties of YBa2Cu3O7-δ compounds. Various nanometer particles;
such as, silicon carbide (SiC), zirconia (ZrO2), yttrium oxide (Y2O3), cerium dioxide (CeO2), tin oxide (SnO2) and aluminum oxide or Alumina (Al2O3) has been reported to
add into YBa2Cu3O7-δ. All of these nanoparticles were acted as additional pinning centre
and resulted in an increase of the JC in higher magnetic fields (Guo et al., 1999, Zhang and Evetts, 1993, Goswami et al., 2007, Lee et al., 2001, He et al., 2001 and Mellekh et
al., 2006). In order to effectively pin the vortices, nanoparticles should possess features
including high density or uniform distribution. Nanoparticles having size of 3-10 nm is
equal to the coherence length (ξ) of YBa2Cu3O7-δ and able to be located at CuO2 planes
(Moutalibi and M‟chirgui, 2007).
Among the added nanoparticles, Al2O3 is more attractive to be selected as the pinning centre material in YBa2Cu3O7-δ. Beside the capability to pin the vortex motions,
Al2O3 nanoparticles are also selected due to its availability in nanometer size, easy fabrication route, higher thermal stability, higher density, better hardness and lower
cost. In 1987, the effects of Al substitution for yttrium (Y) or copper (Cu) sites in
YBa2Cu3O7-δ were accidently found. For long period of high temperature calcination process, the use of alumina crucibles results in the incorporation of Al in crystals having
composition of YBa2Cu3−xAlxOy. X-ray diffraction (XRD) analysis reveals that such substitution does not lead to changes in the structural symmetry of YBa2Cu3O7-δ but the
orthorhombicity of the system is decreased with increasing Al content (Zhang et al.,
2005). The value of TC decreases with increasing Al. This finding was confirmed by Zhang and his colleagues as they purposely added Al2O3 powder into YBa2Cu3O7-δ but
yet no reports have published regarding the ability of Al2O3 particles as pinning centre material. Until Mellekh et al. (2006) revealed that by using the Al2O3 nanoparticles with
